Arrests made in Niger attempted coup, days before President-elect's inauguration

"Several people linked to the coup attempt" have been taken into custody, but authorities are searching for others involved, the source said.

The incident comes two days before the swearing in of President-elect Mohamed Bazoum. The former interior minister succeeds President Mahamadou Issoufou, who stepped down after a decade in power.

Earlier Wednesday, a separate diplomatic source told CNN heavy gunfire was heard outside Niger's presidential palace in an attempted coup, resulting in more than one hour of heavy shelling near the presidency.

Asked to confirm it was an attempted putsch, the diplomatic source said: "Yes it's the army. Which is predominately from the west of the country, which is the heartland of the opposition to Bazoum."

"The government condemns this coward and backwards act that had the intention to attack the democracy and the rule of law that our state has embarked upon as we have seen during these recent elections which were democratic, free and fair and lauded as such by the international community," the statement said.

Both outgoing and incoming presidents were reported to be safe, the source said.

A spokesperson for the UN Secretary-General in New York has said he is "following with great concern the unfolding developments in the country" and "urges all involved to desist from any form of incitement that threatens democratic consolidation and the stability of the country."

CNN has made attempts to reach the Army and Presidency for comment.

The US Embassy in Niger's capital Niamey suspended consular activities and said it would close Wednesday "due to gunshots heard near our neighborhood."

"The security situation throughout Niger remains fluid in the post-election period with the possibility of unrest and/or intercommunal clashes around the country. There may be a corresponding increase in police presence and traffic delays on major roads. Please exercise caution," the embassy said on its website.

The west African nation is in the midst of a security crisis, with a wave of deadly attacks by militants linked to al Qaeda and Islamic State near its borders with Mali and Burkina Faso in recent months.

Last week UN Secretary-General António Guterres strongly condemned "another heinous attack" by unidentified gunmen against civilians in the Tahoua region of the Republic of Niger.

The attack on March 21, reportedly killed at least 137 people, the UN said. It was the second deadly attacks against civilians in recent weeks. At least 58 people including six children were killed in an attack on a market.

Guterres called on countries in the Sahel region to continue their efforts "to address these serious threats to security and stability in the sub-region and beyond".